Certain immunoassays, such as thyroxine (T4) and thyroid stimulating hormone (TSH), have conventionally been done as a wet assay, that is, by using liquid reagents in a cuvette. In one such assay, the enhanced chemiluminescence system originally developed by Amersham International and sold under the tradename Amerlite, the cuvette has an antibody for the target antigen pre-adhered to the cuvette. The liquid sample is added to the cuvette, followed by at least one liquid reagent containing a labeled antibody to the antigen, and the liquid mix is incubated. Following incubation, the mix in the well is aspirated out, followed by multiple washings, to separate bound labeled antibody from unbound labeled antibody. Thereafter, at least one signal generating reagent is added in liquid form to induce enhanced chemiluminescence, which is then read.
All of these steps are time-consuming in their totality. This is handled in the Amerlite system by making the operation a batch operation--the cuvettes are given the sample and first liquid reagent, and incubated, in one apparatus, and then transferred to a different apparatus for washing. Still further, a third apparatus is used for adding the signal-generating reagent and another for reading. In that manner, a first set of cuvettes can be incubating while a second one is being washed and a third is being read, to enhance throughput.
One drawback of such a system is that the three separate stations are not one automated instrument. Other instruments are known that have a single unit to provide incubation and reading, such as is described in German OLS 3,839,080 wherein all incubation functions occur while the cuvette is on a single rotating ring 302. That is, cuvettes 301' have an antibody pre-attached to the wells, p. 9, and the liquid sample, liquid reagents, incubation, washing (station 309) and light-detection (station 325) all occur while the cuvettes are carried around the one ring. However, the provision of all the above-numbered functions in that single incubator ring creates a disadvantage--the throughput is considerably reduced since every step has to occur on the single ring. The washing step alone can take 8 seconds.
The problem, therefore, has been to create an automated analyzer for cuvettes handling liquid reagents, that automates reagent addition, incubation, washing and detection, but with a high throughput not readily provided by an incubator handling all the functions in one rotating support.